1. Field of the Invention
This invention relates to a safety device for an electromechanical opening and closing mechanism such as an automotive sun roof, and more particularly to a safety device which, when a foreign object is caught in the mechanism, interrupts the circuit for driving the mechanism to stop its motion.
2. Description of the Prior Art
The conventional safety device for an electromechanical opening and closing mechanism has been designed to detect a load current in the circuit for driving the mechanism as a load signal and interrupts the circuit when the load current exceeds a set value. For example, in a driving circuit containing a bimetal, when there flows a load current exceeding the allowable current which is determined by the bimetal, the circuit is instantly broken by the bimetal to stop the motion of the above-noted mechanism for preventing damage to the machine or driving circuit being caused by the overload or damage to a foreign object caught in the mechanism which is responsible for causing the overload on the driving circuit. Or, an analog electronic circuit is used for comparing a load signal with a set value. When a load signal exceeds a set value, the analog electronic circuit outputs a signal to the driving circuit for breaking of the circuit.
However, the above-noted conventional safety device has the following disadvantages. First, it cannot follow the variation of a load signal in the normal range and it has a low sensitivity for detection of an abnormal load. This disadvantage is caused by the fact that only one constant value is set as a criterion for detection of an abnormal load.
For example, a slide panel in an automotive sun roof requires a large driving force at the start of sliding when a large frictional resistance is induced. However, once the slide goes into a constant sliding state, only a small driving force is required due to a reduced frictional resistance. Yet, since the above-noted set value is a unvariable one, the set value should be determined to be above the range of the load variation. If the set value is set below the maximum value of the range of the load variation, the safety device will function even though no abnormality has occurred. On the contrary, if the set value is set constantly above the maximum value as described above, the difference between the set value and a signal value related to the load in the above-noted constant sliding state becomes so large that the safety device cannot detect a reasonable abnormality according to a variable load. The device becomes less sensitive.
Even in normal operation, since the frictional resistance exerted on the panel may also vary according to the position of the panel, the load on the slide panel may vary according to the position of the panel along the entire passage. For example, the force required to drive a panel is significantly different when the panel slides normally and constantly, suppresses deflector arms, or seals the opening after it slides over a link.
A second disadvantage of the conventional safety device is its simple function that at an abnormal load it interrupts the driving circuit and only stops the operation of the opening and closing mechanism.
In general, an abnormal load is applied to the opening and closing mechanism when a foreign object is caught or entrapped in the mechanism. Therefore, the foreign object must be removed to eliminate the abnormal load. The removal is generally more convenient when the slide panel is slides back a little before the stoppage of the mechanism. Since the conventional safety device does not have such sliding back function, it is often difficult to remove a foreign object.